Infrared photo-imaging device



Dec. 19, 1961 K. L. KING 3,014,148

INFRARED PHOTO-IMAGING DEVICE Filed April 21, 1958 o zo 34 1 20 m z2 x'ZZ INVENTQR 4e@ A mm mm. o KENNETH Z. K//VG '1 l I BY VZZ Bcv ZZ ZO 0'22 ZZ A-roRNl-:Y

3,ld,l48 Patented Dec. 19, 196i 3,014,148 Hiernaast) nuoro-nakomt;nevica Kenneth L. King, Eastchester, NY., assigner, by mesneassignments, to United Aircraft Corporation, East Hartford, Conn., acorporation of Delaware Filed AprtZl, 1958, Ser. No. '729,748

' 4 Claims. (Cl. 313-67) My invention relates to a photo-imaging deviceand more particularly-to al photo-imaging device which is adapted tooperate in the infrared region of the spectrum.

It is .often desirableto convert a radiation image into an electricalsignal representing the radiation distribution of the image. Theresultant signal may, for example, be applied to a cathode-ray tube toproduce a visual image of the radiation image.

In the prior art devices such as the iconoscope and image orthicon areknown in which a visible image is projected onto a photosensitive mosaicwhich is scanned by an electron beam to produce an electrical signalrepresenting the light distribution of the image. With the present dayimportance of infrared detection, it is desirable that a devicebeprovided for producing an electrical signal representing theenergyldistribution in an infrared image so that a visiblev image of theinfrared radiation image may be produced. It is now known that aphotovoltaic cell sensitive to infrared radiation can be produced on thesurface of a., crystal. The properties ot this cell are deleteriouslyaffected by a rise in temperature resulting from heat energy from anysource other than the image-producing source.

l have invented a photo-imaging device which is especially adapted foruse in the `infrared portion of the spectrum. The photovoltaic elementof my photo-imaging device is shielded from heat energy other than thatemanating from the image-producing areas. I provide my photo-imagingdevicetwith means for maintaining the photovoltaic element at asubstantially constant temperature. l

4 One object of my invention is to provide a photo-imaging device whichis especially adapted for use in the iny frared portion of the spectrum.

Another object of my invention is to provide a photoimaging device forproducing an electrical signal representative of the energy distributionin an infrared image.

A further object of my invention is to provide a photoimaging device inwhich the photo-sensitive element is shielded from radiant heat energyfrom sources other than a target area.

A still further object of my invention is to provide a `photo-iimagingdevice having means for cooling the photosensitive element.

Other and further objects of my invention will appear from the followingdescription.

In general my invention contemplates the provision of an evacuatedenvelope having a surface for supporting a photosensitive mosaic andprovided with means for admitting energy from artarget area. I positionthe mosaic in the path of the energy. I form my envelope with a neckhaving an axis extending in a direction to pass clear of the surface ofthe mosaic. I deflect the electron beam of an electron gun disposed inthe neck to scan the surface of the mosaic. Owing to the disposition ofthe neck with respect to the mosaic surface radiant heat energyemanating from the gun passes clear of the mosaic surface. Electronsfrom the beam which are reiiected from the mosaic surface are collectedby a collector to produce an electrical current which is representativeof the energy distribution in the image projected on the mosaic surface.I provide my device with cooling means for maintaining the mountingsurface of the photosensitive Velement at a substantially constanttemperature.

In the accompanying drawings which form part of the instant specicationand which are to be read in conjunction therewith, and in which likereference numerals are used to indicate like parts in the various views:

FIGURE l is a diagrammatic sectional view of my infrared photo-imagingdevice.

FIGURE 2 is a plan view of a portion of the surface of thephotosensitive mosaic of my infrared photo-imaging device drawn on anenlarged scale.

Referring now to the drawings my infrared photo-imaging device indicatedgenerally bythe reference character lil includes an evacuated envelopei2, one end 14 of which provides a surface i6 on which I mount a crystal13 by any convenient means known to the art such as a suitable adhesive.The crystal 13 may be of any suitable photovoltaic type of sensingmaterial such, for example, as an indium antimonide crystal. l score thesurface of the crystal ld along a plurality of lines to form grooves 2t)which divide the crystal into a plurality of discrete photovoltaic cells22. For example, a one-inch square crystal may be ruled by means of aruling engine or may be photoetched into, for example, LUGO x 1,690elements 22 on a single base. In this manner I form a mosaic ofphotosensitive elements or cells 27. on the surface of crystal id. As isknown in the art, the potential at the surface of each cf the elementsZ2 with respect to the base of the crystal is a function of the radiantenergy falling on the element. lt will be seen that if a radiant imagesuch, for example, as an infrared image, is projectedv on the surface ofcrystal 13 thepotential distribution over the surface of ele-ments Z2will represent the energy distri- Vbution in the image.

I mount a window Zd inthe end 26 of envelope l2 lremote from endi4 toadmit radiant energy from a target area` into the envelope to fall onthe surfaces of elements 22u; produce a potential distribution on thesurfaces of the elements which represents the energy distribution of thetarget image. Window 24 may be formed of any suitable material whichYtransmits infrared radiation, such, for example, as synthetic sapphire.

l form the envelope l2 with an offset neck 2S having an axis indicatedby the broken line A. I mount an electron gun 39 of any appropriate typeknown to the art within neck 23. Respective conductors 32 and 34 connectgun 30 to a suitable source of external potential. Any means known tothe art such as `a deflection yoke indicated generally by the referencecharacter 36 made up of a vertical deiiecting coil 3S and a horizontaldeflectingrcoil 40 may be used to bend the electron beam from gun 3d andto move it across the surfaces of the elements 22 to scan the mosaic 1S.Means such as a coil L41 may be employed to focus the electron beam. As

will be apparent from FIGURE 1 of the drawings, the

.axis A of neck 28 extends in a direction to clear the surface of themosaic element 18. Owing to this disposition of the neck 28, -no thermalradiant energy from the gun 3i) is permitted to reach the elements 22.Thus I have avoided the deleterious eiects of thermal radiant energyfrom the gun reaching the elements 22.

I provide the end i4 with a cooling block 42 which may, if desired, beintegrally formed with end 14. A serpentine passage 44 in block d2permits the passage of cooling fluid lthro-ugh the block.y A pipe i6admits a suitable cooling iiuid such, for example, as liquid nitrogen tothe passage 4,4. A pipe 48 connected to the outlet of passage ed permitscooling fluid introduced into the passage to iiow back to the source(not shown) of iiuid. The cooling duid passing through the block 42maintains the temperature of the crystal i8 substantially constant toensure that its photovoltaic properties remain substantially constant tooperate effectively in the infrared band of the spectrum.

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As has been explained hereinabove, a radiant image projected onto thesurfaces of elements 22 produces a potential distribution on thesesurfaces, which distribution represents the energy distribution of theimageproducing area. As the electron beam from gun 30 strikes thesurface of an element 22, respective percentages ofthe electrons areabsorbed and rellected depending upon the potential of the surface oithe element with respect to the base of crystal t6. Since the surfacepotential of an element 22. is a function of the radiation falling onthe element, the number of electrons reflected will be some function ofthe energy falling on the element. I mount a collector 5G Withinenvelope 12 by any convenient means known to the art. A terminal 52extending through the wall of envelope 12 provides a connection forcollector 50 to `a suitable source of potential. Electrons reflectedfrom the surface of an element 22 are collected by collector Sti toproduce a current in the external circuit which is proportional to thelight energy impinging `on the element. As the beam from gun Si) scansthe surfaces of elements 22, a current flows in the external circuitwhich is representative of the potential distribution on the surfaces ofelements 2?, and thus representative of the energy distribution in thetarget area. It will be obvious that the surface of crystal 18 must bescored to produce the mosaic elements 22 if the result described aboveis to be achieved.

In operation of my photo-imaging device I project a radiation imagesuch, for example, as an infrared image onto the elements 22 by anyconvenient means known to the art. As a result, the potentialdistribution on the surfaces of elements 22 is representative of theenergy distribution of the target area. As the beam 30 scans theelements 22 percentages of electrons from the beam are reflected andcollected by collector 56 to produce an external circuit currentrepresenting the energy distribution of the target area. 28 with respectto the element 1d radiant thermal energy from gun 30 is prevented fromfalling on the elements 22 to give a false indication in the externalcircuit. At

the same time the cooling liquid passing through block 42 maintains theVtemperature of crystal 18 substantially constant -to maintainsubstantially constant the photovoltaic properties of the elements 22.

While I have described my photo-imaging device as being especiallyadapted for use in the infrared band of the spectrum, it is to beunderstood that it functions as well in other bands or" the spectrumsuch, for example, as the visible band. v

It will be seen that I have Iaccomplished the objects of my invention. Ihave provided a photo-imaging de- Vvice for producing an electricalsignal representing the energy distribution in a target area. My deviceis particularly adapted for use in the infrared band of the spectrum. Ishield the mosaic of my device from radiant thermal energy from theelectron gun producing the scan- Owing to the disposition of neck i ningbeam. Cooling means maintains the temperature of my mosaic crystalsubstantially constant.

IIt will be understood that certain features and subcombinations are ofutility 'and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of myclaims. It is further obvious that various changes may be made in`details within the scope of my claims Without departing from the spiritof my invention. It is, therefore, to be understood that my invention isnot to be limited to the speciic details shownv and described.

Having thus described my invention, what I claim is:

1. A photo-imaging device including in combination an envelope having abody providing .a mounting surface and a neck having a Wall and having alongitudinal axis, a photo voltaic mosaic element, means carried by saidenvelope for admitting radiation into said envelope, means mounting saidmosaic element on said mounting surface in a position to receiveradiation admitted into said envelope, said neck being so disposed withrespect to said body that its axis extends in la direction to clear thesurface of said element, an electron gun for producing a beam ofelectrons, means mounting said gun in said neck in 4a position at whichany straight line from said gun to said element intersects said neckWall to cause said neck to intercept thermal radiation emanating fromsaid gun in the direction of said element, means for causing said beamto scan the surface of said photo voltaic mosaic, means for collectingelectrons reflected from said element surface and means for cooling saidsurface by conduction.

2. A photo-imaging device as in claim l in which said element is amosaic formed with a plurality of photovoltaic cells.

3. A photo-imaging device as in claim 1 in which said element is anindium antimonide crystal scored to form a plurality of mosaic cells.

4. A photo-imaging device as in claim l in which said cooling meansincludes a cooling block and means for passing a coolant through saidblock.

References Cited in the file of this patent UNITED STATES PATENTS2,241,974 Anderson May 13, 1941 2,441,971 Litton May 25, 1948 2,538,852Szegho Jan. 23, 1951 2,622,226 Thiele Dec. 16, 1952 2,691,612 Cayen Oct.12, 1954 2,716,203 Sen Aug. 23, 1955 2,739,244 Sheldon Mar. 20, 19562,802,963 Sheldon Aug. 13, 1957 FOREIGN PATENTS 902,278 Germany Jan. 21,1954 1,084,262 France Jan. 18, 1955

